In military applications, secure and covert identification of an asset as friend or foe, also referred to as Identification Friend or Foe (IFF) is of the utmost importance. Indeed, it is primordial for military platform commanders to be able to accurately distinguish friendly aircrafts, vehicles, or forces from the enemy in order to prevent accidental fratricide (friendly casualties due to friendly fire). This becomes increasingly difficult when forces move covertly through unknown combat zones with limited visibility.
As known in the art, modern technology, and optical IFF systems in particular, ensures that action against friendly forces is reduced or prevented by visually identifying potential targets as friend or foe. Typically, optical IFF emitters used for such identification operate in the near Infrared (near-IR) wavelengths, i.e. between 0.7 and 1.3 micrometers (μm), a range very close to visible light. Although the radiation they emit is invisible to the human eye, a major disadvantage of these emitters is that they are highly visible via night vision systems (NVS), which are commonplace in military applications. NVS are optical systems, which allow images to be produced in levels of light approaching total darkness.
Thermal imaging provides an alternative to near-IR systems by enabling the location of living and inanimate bodies otherwise hidden to be revealed through their heat signatures. This is done by visualization of the battlefield with a thermal imaging device. These devices are sensitive to radiation emitted in the infrared range of the electro-magnetic spectrum. However, one drawback of thermal imaging systems is that they typically do not allow to identify and detect the bulk of a scene's distinguishable characteristics (i.e. people, places, or objects). In particular, in military applications, an observer cannot determine whether the displayed thermal image represents a “friendly” soldier (i.e. on their team) or an enemy as only the heat generated by the soldier is imaged on the thermal imaging device.
To overcome these and other drawbacks of existing optical IFF systems, the prior art reveals thermal beacons, which are used for friend or foe identification through a thermal imager and is otherwise invisible to the naked eye and near-IR imaging equipment. Such a beacon typically emits a continuous series of flashes visible to far-IR imaging equipment when in operation and is attached to each friendly asset, thus allowing for covert identification when the beacon is in operation. One drawback of such prior art thermal beacons, however, is that they typically rely on heating a blackbody (such as conductive plate or the like) to generate emissions in the infrared range. As a result, a significant delay is typically experienced between successive beacon flashes as the beacon is heated and subsequently cooled and as a result is typically unsatisfactory for signalling applications without the use of a complex shuttering system. Another drawback of such prior art devices is that blackbody radiation is inherently omnidirectional in nature and as a result the distance over which the beacon can be detected by the IR imaging equipment is limited. Still another disadvantage is that even if the beacon is proximate enough that it can be detected using the IR imaging equipment, the image presented to the operator on the display of the equipment as a result of the radiation emitted by the beacon is small relative to the entire field of view (in many cases just a single pixel) and therefore may go undetected by all but the most vigilant of operators.